Long-duration space missions require electrical power sources for on-board systems. The electrical power sources must operate reliably for long periods of time using little fuel. Such electrical power sources are to be distinguished from the propulsive engines. Long-duration space missions include, for example, deep-space missions, interplanetary missions, and long-term earth-orbit missions. The electrical power sources must also be relatively light in weight, as they must be initially lifted to orbit.
Solar electrical power sources are widely and successfully used for earth-orbit missions, such as geosynchronous communications satellites. The solar power sources are not practical for deep-space missions and for many lower-orbit missions.
Another approach to such a long-term power source has been small nuclear reactors. A variation of the conventional nuclear reactor favored at the present time for some applications is the Radioisotope Thermoelectric Generator (RTG), which uses the heat produced by fission of fuel to heat a thermopile. The thermopile includes an array of thermocouples which produce an electrical voltage responsive to the heating. In each of these cases, the fuel mass requirement is relatively large. The current version of the RTG utilizes about 10 kilograms of uranium to produce about 60 amperes of current. That is, a large weight of fissionable material must be launched into space on a booster rocket. In addition to the amount of weight that must be lifted, there is an environmental concern with the amount of uranium that is potentially scattered in the event of a booster failure. Additionally, the large amount of excess waste heat generated by such power sources must be radiated into space by large radiators located on the spacecraft, which add to the weight of the spacecraft. An effort is made to radiate the heat uniformly, but there have been indications that slight asymmetries in the amounts of heat radiated in different directions can lead to changes in the velocity of the spacecraft, throwing it off its intended course or orbit.
There is a need for an improved approach to the generation of electrical power for long-duration space missions, particularly deep-space missions. The approach must meet the power requirements, and desirably would overcome or minimize the problems associated with existing power sources. The present invention fulfills this need, and further provides related advantages.